The present invention is directed to elongated intracorporeal devices, and more particularly intraluminal devices for stent deployment, percutaneous transluminal coronary angioplasty (PTCA), and the similar procedures. PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient's coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient's artery to open up the arterial passageway and increase the blood flow through the artery. To facilitate the advancement of the dilatation catheter into the patient's coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique through the brachial or femoral arteries. The catheter is advanced therein until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient's coronary artery until the balloon on the catheter is disposed within the stenotic region of the patient's artery.
Once properly positioned across the stenosis, the balloon is inflated one or more times to a predetermined size with radiopaque liquid at relatively high pressures (e.g., generally 4-12 atmospheres) to dilate the stenosed region of a diseased artery. After the inflations, the balloon is finally deflated so that the dilatation catheter can be removed from the dilatated stenosis to resume blood flow.
Similarly, balloon catheters may be used to deploy endoprosthetic devices such as stents. Stents are generally cylindrical shaped intravascular devices that are placed within a damaged artery to hold it open. The device can be used to prevent restenosis and to maintain the patency of blood vessel immediately after intravascular treatments. Typically, a compressed or otherwise reduced diameter stent is disposed about an expandable member such as a balloon on the distal end of the catheter, and the catheter and stent thereon are advanced through the patient's vascular system. Inflation of the balloon expands the stent within the blood vessel. Subsequent deflation of the balloon allows the catheter to be withdrawn, leaving the expanded stent within the blood vessel.
Typically, the distal section of a balloon catheter or other percutaneous device will have one or more radiopaque markers in order for the operator of the device to ascertain its position and orientation under X-ray or fluoroscopy imaging. Generally, a band or ring of solid radiopaque metal is secured about an inner or outer shaft of a balloon catheter to serve as a radiopaque marker. Such configuration, however, locally stiffens the catheter shaft and thereby imparts an undesirable discontinuity thereto as the solid metal bands are relatively inflexible compared to a polymer balloon catheter shaft. Additionally, the metallic markers are relatively expensive to manufacture and relatively difficult to positively affix to an underlying device.
As is described in U.S. Pat. No. 6,540,721, which is incorporated herein by reference, many of the problems associated with the use of conventional markers may be overcome by replacing the rigid precious metal tubing with a polymer that is filled or doped with a suitable radiopaque agent. Such marker may be formed by blending a polymer resin with a powdered, radiographically dense material such as elemental tungsten and then extruding the composition to form a tubular structure with an appropriate inner diameter and wall thickness. The extrusion may then be cut to discrete lengths and installed onto the intended component via a melt bonding process.
A shortcoming of such an approach has been found to be the apparent limit to which a suitable polymer can be filled with a radiographically dense material to yield a composition that can be successfully compounded, economically shaped into suitable dimensions for markers and easily assembled onto a component without unduly compromising the desirable properties of the polymer matrix. The fill ratio that is achievable will determine how thick a marker must be in order to achieve a particular degree of radiopacity. In the case of tungsten in a polymer such as Pebax (polyether block amide), the fill ratio limit has heretofore been found to be about 80 weight percent. Such weight percentage equates to about 18 volume percent which requires the marker to be excessively thick in order to achieve adequate radiopacity.
A polymeric marker is therefore needed having a substantially higher fill ratio than has heretofore been possible. Such marker would allow devices to be rendered highly visible without an inordinate increase in overall profile nor a compromise of the flexibility of the underlying component.